Speed Control Of Three Phase Induction Motor By Employing Modified Sepic Converter

Abstract

This project is used to control the speed of three phase induction motor by employing modified sepic converter. The modified sepic converter is used to boost the input voltage. The boosted dc voltage is applied to the three phase inverter. This three phase VSI operates at 120 degree mode of operation. Three phase induction motor speed depends on the frequency of inverter.

Introduction

This project is mainly used for renewable energy source like solar, wind etc. The solarconverts the sunlight directly into electricity. That voltage range is low, so that low voltage is boosted by using the converter circuits. Converter is used to convert the low voltage dc into high voltage dc. Solar energy is involved in power plants, homes made appliances, ventilation systems, commercial appliances, solar lighting, cars and other remote applications where transmission and distribution is done.

Proposed System

The modified sepic converter has two inductors and one power devices for boosting the input voltage. If the power device duty cycle is varied the output voltage of the converter is also varied. The converter output dc voltage is applied to the three phase inverter circuit. It converts the dc voltage into three phase ac voltage to drive the three phase induction motor. The PIC controller has key function for controlling the speed of the induction motor.

Block Diagram

Block Diagram Explanation

Pulse generator: - Here we have used PIC microcontroller (PIC 16F877a) to

generate PWM signal.

Driver circuit: It is used to amplify the pulses and provided isolations using

opto coupler. It has two functions,

Amplification

Isolation

Bridge Rectifier: It converts AC supply to DC Supply.

MODIFIED SEPICconverter: It converts low voltage DC to high voltage

DC supply.

Three Phase Inverter: It converts DC supply tothree phase AC Supply to

drive the three phase induction motor.

Driver Board

Pic Controller Board

Working

The PIC controller is used to generate the PWM pulses for converter and

inverter circuit. The PIC controller pulses are given to the driver circuit as input.

Driver board is mainly used to isolate and amplify the input signals from the

controller. The amplified driver output is connected to the main power circuit

devices. The ac supply is converted into dc by using bridge rectifier. And the dc

voltage is boosted by using modified sepic converter. The boosted dc voltage is

applied to inverter circuit and by varying the frequency of the inverter the motor

speed also varied.

Circuit Diagram For Modified Sepic Converter

Circuit Diagram For Three Phase Inverter

Advantages

High efficiency

Easy to control the speed

Switching losses are reduced

Applications

Industrial applications Pumping system

Conclusion

The speed control of three phase induction motor by employing modified sepic converter is mainly used to convert the low voltage sources to useful voltage source. The solar voltage produced is low voltage and themodified sepic converter is used to boost the low voltage and applied the dc voltage to three phase inverter circuit. So that low voltage solar energy is used to control the induction motor speed.

Output Waveform For Modified Sepic Converter

Three Phase Inverter Pattern